ABSTRACT
Over the last decade, the phenomenon of organic products has taken hold of large segments of consumers. At its most basic level, organic wine is made from grapes that have been grown with as little human impact as possible. Organic wine is a wine obtained from organically growing grapes without the help of or need for synthetic fertilizers, synthetic plant treatments, or herbicides (Trioli and Hofmann, 2009). Accurate studies have been carried out on soil and vineyard management in organic wine making whereas, as far as we know, no or few data are available on microbial populations of grape berries from organic vineyard as well as of those from organic wines. In a previous paper (Tofalo et al., 2011) the yeast
populations present on grape berries and must from organic vineyards of red Montepulciano d’Abruzzo and white Trebbiano cultivars were studied. In particular non-Saccharomyces (NS) wine yeasts were identified at species level. Moreover the strains were typed and characterized for some oenological parameters. In recent years, a lot of studies evaluated the NS species present in wine ecosystem, and demonstrated the impact of grape conditions on NS populations (Fernández et al., 2000; Raspor et al., 2006; González et al., 2007). The role of NS yeasts in wine production has been debated extensively and several researchers have shown that NS yeasts survive during fermentation and could reach cell concentrations similar to those reached by Saccharomyces cerevisiae 106-108 cells/ml (Fleet et al., 1984; Gafner and Schultz, 1996). In fact, as suggested by several authors (Zironi et al., 1993; Gil et al., 1996; Lema et al., 1996; Toro and Vazquez, 2002; Ciani et al., 2006; Viana et al., 2008), there is growing evidence that NS yeasts play an important role in wine quality. Fleet (2008) discussed the possibilities of using yeasts other than those from the genus Saccharomyces for future wine fermentations and the commercial viability of mixed cultures, because NS species have great potential to introduce appealing characteristics to wine that may improve its organoleptic quality. Consequently, the impact of NS yeasts on wine fermentation cannot be ignored. The major NS yeasts present during organic must fermentation of Trebbiano and Montepulciano cultivars were Hanseniaspora uvarum, Metschnikowia fructicola and Candida zemplinina, representing 43, 31 and 11%, respectively, of the total NS population isolated. Although the population size of these species was reduced throughout the wine fermentations, their growth was not completely suppressed and NS yeasts were still present at the end of the fermentation process (Tofalo et al., 2011). These yeasts from organic wine shared many characteristics which suggest that the strong selection pressure exerted by farming system and vine variety could have generated variability at different levels. Knowledge about the biodiversity of native yeasts is essential for the preservation and exploitation of the oenological potential of wine grape growing regions. The use of a selected multistarter (controlled mixed cultures) was proposed several years ago. In the middle of the last century, to reduce the acetic acid content of wine, Cantarelli (1955), Castelli (1969) encouraged the sequential use of Torulaspora delbrueckii (formerly known as
Saccharomyces rosei) and S. cerevisiae. Later on, mixed cultures were proposed also for other objectives such as the biological deacidification of must or increase the glycerol content but one of the most investigated uses of mixed cultures relates to confer greater complexity to a wine, enhancing its organoleptic profile (Ciani et al., 2010). Several studies on mixed fermentations containing S. cerevisiae and NS wine yeasts have been carried out to evaluate the possibility of using controlled multistarter cultures to improve wine quality (Mora et al., 1990; Zironi et al., 1993; Toro and Vazquez, 2002; Ciani et al., 2006; Andorrà et al., 2010). For this purpose different NS species were used to study mixed fermentation such as Hanseniaspora guilliermondii, H. uvarum, Candida pulcherrima (Metschnikowia), Pichia kluyveri, Pichia fermentans, Candida cantarellii, T. delbrueckii, Kluyveromyces thermotolerans, Candida stellata (recently reclassified as Starmerella bombicola). The yeasts present on grape berries and must from organic vineyards could have a unique composition and these indigenous yeasts impart distinct regional and desired characteristics to wines. In this context, autochthonous NS strains could be selected to conferment organic musts alongside S. cerevisiae.
